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IAPRS & SIS, Vol.34, Part 7, "Resource and Environmental Monitoring", Hyderabad, India,2002 
  
In this context a study was carried out to i) analyse the within 
filed variability of crop and soil parameters derived from direct 
measurement and through spectral measurements, using ground 
truth spectroradiometer and satellite based data, ii) to derive the 
relationship between both narrow band and broad band spectral 
data with field crop and soil parameters. This study was carried 
out in well-managed agricultural farm 
2. STUDY AREA 
The study was carried in the farm of Central Potato Research 
Station (31.16°N latitude and 75.32°E longitude) in Jalandhar, 
Punjab state of India. IRS 1C Pan data of the farm during 23 Feb, 
2002 shows the layout of the farm (Figure 1). The farm follows 
potato-wheat crop rotation. The study was carried out for during 
wheat crop growing period. The study was carried out in two 
fields. In the first field (4.15 ha), where wheat was being grown, 
experiment was carried to study the crop variability. In the second 
field (4.43 ha), where potato had been harvested and the land was 
fallow, the experiment was carried out to study soil variability. 
The soil type of the farm was ranging from very deep sandy loam, 
very deep loam to very deep clay loam. 
  
Figure 1. IRS pan image of the CPRS farm and its surrounding (1, 
2 are the fields where crop and soil variability, 
respectively, were studied) 
3. METHODOLOGY 
3.1 Collection of Field parameters 
The study was carried out during the rabi (winter) crop season of 
2001-02. The soil parameters measured included 35 observations 
at fixed grid locations from a field of 4.43 ha for organic carbon, 
availability of nitrogen, phosphorus and potassium. Table 1 
shows the methodologies followed for measuring these 
parameters. The plant parameters included 30 observations at 
fixed grid locations from field of 4.15 ha for leaf area index (LAI), : 
biomass at harvest and yield of wheat crop. The LAI was 
measured during soft dough stage of wheat crop, in a non- 
destructive approach, using Sunscan Canopy Analysis System, 
manufactured by Delta T Devices. Crop yield and biomass 
measurements were collected using crop-cutting experiments. 
Table 1. Methodology for determining soil chemical parameters 
  
  
  
  
  
  
  
  
  
Parameter Method Reference 
Organic Carbon Chromic acid titration Walkley and 
method Black (1934) 
Available N Alkaline Permanganate Subbiah and 
Extractable Method Asija (1956) 
Available P Sodium Bicrabonate Olsen et al. 
Extractable Method (1954) 
Available K Ammonium acetate Muhr et al. 
(Exch.+ Soluble) Extractable Method (1965) 
  
3.2 Collection of Field Spectral Data 
Spectral data for crop and soil were collected, at the above grid 
locations, using a 512 channel spectroradiometer with a range of 
350 nm to 1800 nm, manufactured by Analytical Spectral 
Devices, Inc (FieldSpec®Pro, 2000). The instrument acquires 
hyperspectral data at the spectral resolution of 3 nm at 700 nm 
and 10 nm at 1400 nm. The sampling interval is 1.4 nm for the 
spectral region 350-1000 nm and 2 nm for spectral region 1000- 
1800 nm. Gathering spectra at a given location involved 
optimizing the integration time (typically set at 17 ms), providing 
foreoptic information, recording dark current, collecting white 
reference reflectance and finally, obtaining the target reflectance. 
The target reflectance is the ratio of energy reflected off the target 
(e.g. crops) to energy incident on the target (measured using 
BaSO4 white reference). Since the dark current varies with time 
and temperature, it was gathered for each integration time 
(virtually for each new reading). The instrument comes with a 
window-based software ViewSpec Pro (Ver. 2.10) for viewing, 
analysing and exporting the spectral data. Data was collected for 
each grid point both from cropped field and fallow land (for soil). 
For each grid point two reflectance measurements were collected, 
along a transect, with a nadir view from a height of 1.3 m above 
ground for crop and soil using 25? FOV (Field of View). The 
spectral data for the cropped field was collected concurrent to the 
LAI observations. 
3.3 Analysis of Field Spectral Data 
Since we had thirty grid points for the cropped field and thirty 
five grid points for the soil, we got as many number of spectral 
profiles (after averaging the two measurements of each point) and 
each profile contained 1471 data points. Thenkabail et al (2000) 
. have found that optimum narrow-band width for biophysical 
studies to be 15 nm. Hence the spectral data was aggregated 
(averaged, assuming the spectral variation to be linear in the 15 nm 
interval) to 15 nm intervals, reducing the number of data points to 
98 in each profile. Thenkabail (2002) have found that the best four